Thermal barrier coatings (TBC) are used to provide thermal protection for metallic components exposed to the hot gas path of a gas turbine engine. A typical component may include a superalloy substrate material coated with a layer of MCrAlY bond coat material and a top coating of a ceramic material such as yttria stabilized zirconia (YSZ). During operation of the gas turbine engine, such coatings experience degradation due to wear, erosion, foreign object damage, cracking and spallation. When the coating thickness decreases below a critical dimension or its properties are otherwise degraded to a critical degree, the protection provided by the coating is no longer adequate and the underlying substrate material can be degraded by the hot combustion gas environment. Repair of such coatings typically requires the complete removal of the ceramic material and bond coat and the application of a new coating.
TBC removal is typically accomplished using some combination of autoclave, caustic and acidic solutions, and mechanical abrasion such as grit blasting. Such methods create potentially hazardous waste products, and may have detrimental effects on the underlying substrate material, such as by increasing the diameter and eroding the shape of cooling holes formed through the substrate.
Laser energy has been used for the cleaning of turbine components, for example as taught in U.S. Pat. No. 6,759,627. United States Patent Application Publication No. US 2010/0224601 A1 describes the removal of a thermal barrier coating from a turbine component by using pulsed laser energy to create mechanical shock waves within the coating which crack and remove the coating without deforming the underlying substrate. However, laser removal of TBC's has not achieved wide use in the industry.